Lightroom 4.1: Sluggish, Freezes constantly, Blurry Thumbnails

These have probably been all covered before but after spending hours trying to sort out my issues I don't have time to read through everyone elses. I waited patiently for the 4.1 RC and that solved my External Editor problem. But that's about all it solved.

I continue to have:
- Extremely Sluggish. Takes forever to load. 3.6 was like lightning. This is like molasses.
- I had 4 fatal system crashes today in the first half hour I went to use LR4.1RC. I never had this before.
- Although photos load in split seconds and crystal clear in Windows Preview or other apps, they take forver to load in LR. The little spinning "Loading" at the bottom of the images keeps on going, and going, and going, .....
- Images (.jpg - 5184x3456 18mp) over maybe 6mb or so (18mp) many times have blurry thumbnails even when I have them set for the largest settings. And that's if they load.

So I was trying to hold off and not go back but at this point I am going back to 3.6. I don't have time for this. And that's after I asked before puchasing 3.6 if there was a free upgrade to LR4 and was told "maybe" (4 was in beta and nearing release). I then find out I had to pay for the upgrade because of a few days.